The disclosure of Japanese Patent Application No. 2000-292979 filed on Sep. 26, 2000 is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a drive unit for a parallel-type hybrid vehicle wherein an engine and a motor are coupled for use as a power source, and more particularly to a hybrid-vehicle drive unit wherein a motor is fitted to an automatic transmission having a hydraulic power transmission.
2. Description of Related Art
Japanese Patent Application Laid-Open No. (xe2x80x9cKokaixe2x80x9d) HEI 9-215270, discloses a drive unit for a parallel-type hybrid vehicle wherein a motor-generator is fitted to an automatic transmission equipped with a torque converter. The driving force of the motor-generator assists the driving force of the engine e.g. when the vehicle starts from a standstill or is accelerated. The motor-generator functions as a generator to supplement the effect of the engine brake when the vehicle runs down a slope or is braked, and wherein braking energy is regenerated to improve fuel efficiency and reduce exhaust emissions. Similar hybrid vehicle drive trains are disclosed in Japanese Patent Application Laid-Open No. (xe2x80x9cKokaixe2x80x9d) HEI 5-30605, and Japanese Patent Application Laid-Open No. (xe2x80x9cKokaixe2x80x9d) HEI 5-024447.
According to Kokai 9-215270, a motor housing for a motor-generator is sandwiched between an engine and a transmission housing containing the transmission and a torque converter. According to Kokai 5-30605, a motor-generator is disposed in a bypass between a turbine runner and a pump impeller of a torque converter. According to Kokai 5-024447, a motor-generator is directly mounted radially outside of a torque converter. Namely, the motor-generator is disposed in an automatic transmission that has substantially the same structure as a conventional automatic transmission, with a rotor supported radially outward of the cover of the torque converter.
In an internal combustion engine, pistons reciprocate due to explosive combustion of a fuel-air mixture in cylinder chambers to rotate a crank shaft. However, vibrations due to combustive explosion cause the crank shaft to rotate eccentrically (with deflection), preventing centering precision.
On the other hand, the efficiency of the motor-generator is enhanced in proportion to a decrease in clearance (air gap) between its stator and rotor, which, in turn, requires an increase in precision in radial support of the rotor, i.e., centering precision. Further, since the output of the motor-generator increases in proportion to an increase in the axial length of opposing surfaces of the stator and the rotor, the efficiency of the motor-generator is also greatly affected by precision in axial support of the rotor.
If the rotor is directly coupled to the crank shaft as in Kokai 9-215270, centering precision of the crank shaft directly affects centering precision of the rotor. Thus, the rotor needs to have an excess of air gap corresponding to the degree of eccentricity caused by explosive vibrations. Thus, the motor-generator decreases in efficiency, and requires a corresponding larger capacity.
Further, if the motor-generator is disposed between the turbine and the front cover of the torque converter as disclosed in Kokai 5-30605, the front cover is directly coupled with the crank shaft. Thus, centering precision of the crank shaft directly affects precision of the support position of the rotor. Also, since the torque converter undergoes deformation such as expansion or contraction due to changes in inlet pressure and centrifugal hydraulic pressure, the stator fixed to the pump impeller and the rotor fixed to the turbine runner are axially displaced relative to each other, and the motor suffers a corresponding decrease in efficiency. Thus, in order to obtain the required output, to offset the decrease in efficiency of the motor-generator, the motor-generator must be enlarged.
Further, if the motor-generator is directly mounted radially outside of the torque converter as disclosed in Kokai 5-024447, it is difficult to enlarge the diameter of the motor-generator owing to spatial restrictions such as vehicle height. It is difficult to provide a motor (generator) having the necessary output torque within such a limited space. Further, since the rotor of the motor-generator is directly supported radially outside of the cover of the torque converter, when the torque converter undergoes deformation, i.e., expansion or contraction due to changes in inlet pressure or centrifugal hydraulic pressure, there is the possibility of interference between the stator and the rotor. Thus, the rotor needs an excessive air gap corresponding to the expansion or contraction of the torque converter and the efficiency of the motor-generator is thereby decreased and requires a corresponding increase in capacity.
Further, the torque converter generates a great amount of heat. Thus, if the torque converter is integrated with the rotor, the permanent magnet of the motor may by demagnetized by heat from the torque converter. Furthermore, if the lock-up clutch and the rotor are located close to each other, the cover integrated with the rotor is magnetized due to the magnetic flux emitted from the permanent magnet of the rotor. As a result, iron powder dispersed in hydraulic fluid in the torque converter may accumulate in the lock-up clutch and obstruct operation of the lock-up clutch.
Thus an object of the invention is to provide a hybrid-vehicle drive unit capable of supporting a motor-generator with high precision, improving the efficiency of the motor-generator, and reducing the size of the motor-generator with independence from the influence of centering precision of the crank shaft of an engine, from deformation of the hydraulic power transmission, and so on.
To achieve the above-stated object, according to one aspect of the invention, there is provided a hybrid-vehicle drive unit comprising an engine, an automatic transmission having a hydraulic power transmission and an automatic speed-change mechanism, and a motor having a stator and a rotor that is coupled to an input section of the hydraulic power transmission. A motor housing for the motor is disposed between a housing of the hydraulic power transmission and the engine. The stator is fixed to the motor housing. The rotor is rotatably supported by the motor housing, and is disposed radially outside of the hydraulic power transmission with a predetermined clearance.
In the above arrangement, the rotor of the motor is independently supported by the housing of the motor, e.g., via the bearing, isolated from any affect of eccentric rotation of the crank shaft resulting from explosive vibrations of the engine or deformation of the hydraulic power transmission resulting from changes in inlet(charging) pressure or centrifugal hydraulic pressure.
According to the above aspect of the invention, the motor is separated with the stator fixed to the motor housing and with the rotor rotatably supported by the motor housing, and a predetermined clearance is left between the rotor and the torque converter. Thus, it is possible to provide support with high centering precision without influence by eccentric rotation of the crank shaft. The above-described construction also ensures a clearance (air gap) of high precision by preventing the rotor and the stator from interfering with each other due to expansion or contraction of the torque converter caused by changes in centrifugal hydraulic pressure and so on. Thus, the efficiency of the motor can be enhanced by narrowing (decreasing) the clearance, and the functions as described above can be performed reliably with a relatively compact structure. Further, since the predetermined clearance exists between the rotor and the torque converter, the permanent magnet is prevented from demagnetizing due to generation of heat within the torque converter. Furthermore, since the lock-up clutch and the rotor, which are disposed in the front cover of the torque converter, are located far from each other, trash such as iron powder can be prevented from flaking off the permanent magnet of the rotor and accumulating in the lock-up clutch. Thus, the lock-up clutch can operate without hindrance.
In the above aspect of the invention, the hydraulic power transmission may have a lock-up clutch and a front cover that is integrated with an outer shell of a pump impeller and that covers a turbine runner and the lock-up clutch, and a supporting member for supporting the rotor may be provided on the engine side of the front cover with a predetermined clearance and may be rotatably supported by a bearing fitted to the motor housing.
According to this construction, the motor is separated from the hydraulic power transmission by the front cover and isolated from hydraulic fluid in the hydraulic power transmission. Therefore, the motor can be prevented from loss of efficiency due to contact with the hydraulic fluid. Furthermore, the rotor is supported by the supporting member spaced from the front cover by the predetermined clearance. Thus, the influence of deformation of the hydraulic power transmission resulting from changes in charging pressure or centrifugal hydraulic pressure can be eliminated more reliably. By increasing the axial length (cumulative thickness) of the rotor, the required performance of the motor as described above can be guaranteed without increasing the dimensions of the motor.
In the above aspect of the invention, the motor housing may have a lateral wall that defines the engine side of the motor, and the bearing may be fitted to a radially innermost (distal) end of the lateral wall. The supporting member for supporting the rotor may be coupled to the front cover. According to this construction, the motor is separated on the engine side by the lateral wall, and the bearing for supporting the rotor is fitted to the distal end of the lateral wall. Therefore, the motor is covered on the engine side thereof with the lateral wall and thus is protected from water and dust. Thus, the lateral wall serves as a cover as well as the rotor supporting member, whereby the drive unit can be made compact as a whole.
In the above aspect of the invention, the hydraulic power transmission may have a front cover that is integrated with an outer shell of a pump impeller and that covers a turbine runner. A center piece may be integrated with the front cover, and may be opposed to a crank shaft of the engine with a clearance therebetween or the center piece and the crank shaft may be coupled with each other via an impact absorbing member.
In the latter construction, the center piece and the crank shaft are separated from each other by the clearance with their edges cut off, and are coupled with each other by the impact absorbing member. Therefore, explosive vibrations of the engine are absorbed by the impact absorbing member and thus are prevented from being propagated toward the rotor, so that high precision in support of the rotor is guaranteed. Also, the radial load applied to the bearing is reduced, whereby durability of the bearing can be improved.
In the above aspect of the invention, the center piece may be spline-fitted with a plate hub that is linked with the crank shaft via the impact absorbing member, and the spline-fitting may be a press-fit engagement of a lead spline with a straight-tooth spline. According to this construction, the plate hub and the center piece are integrated with each other with no play therebetween through press-fitting engagement of the splines. Thus, fretting abrasion otherwise produced by explosive vibrations of the engine can be prevented.
In the above aspect of the invention, a hub of the supporting member for supporting the rotor may be fitted to the center piece. The hub of the supporting member may be fastened by a nut screwed onto threading formed in the center piece, and may be integrally press-fitted to and coupled with the front cover. Thus, fretting abrasion due to looseness between the tooth flanks of the splines can be prevented. The motor-generator can be reliably protected from adverse affect of aerugo powder and so on.
In the above aspect of the invention, the hydraulic power transmission may be interposed between a crank shaft of the engine and an input shaft of the automatic speed-change mechanism and may have a lock-up clutch that connects a turbine runner with a pump impeller. The lock-up clutch may be located closer to the engine than the torus of the hydraulic power transmission and may have a smaller diameter than the outside diameter of the torus. The motor may be disposed radially outward of the lock-up clutch at a position that at least partly axially overlaps the lock-up clutch.
According to this latter construction, since the motor is disposed so as to axially overlap with the lock-up clutch, the overall axial dimension need not be lengthened, and thus good mountability on the vehicle is guaranteed. Also, since the motor is disposed radially outward of the lock-up clutch, i.e., at a position closer to the engine than the torus of the hydraulic power transmission, the hydraulic power transmission can be ensured of a sufficient capacity. Further, the motor is ensured of good mountability on the vehicle, e.g., sufficient road clearance, and has an appropriate radial dimension. Sufficient output of the motor is guaranteed, whereby the starting performance and the vehicle driving performance of the engine can be improved.
The lock-up clutch may be a multiple-plate clutch which allows the lock-up clutch to be reduced in diameter to accommodate the motor disposed radially outside thereof. Because the lock-up clutch is a multi-plate clutch, sufficient torque capacity can be guaranteed.
The lock-up clutch may have a spring damper composed of circumferentially arranged coil springs, and the spring damper may be disposed radially inside the frictional plate portion of the lock-up clutch at such a position that at least part of the spring damper axially overlaps the lock-up clutch. According to this construction, the spring damper is disposed radially inside of the friction plates of the lock-up clutch. Because no additional axial dimension to accommodate the spring damper is required, the drive unit need not be increased in total length.
In the above aspect of the invention, the hydraulic power trans mission may have a front cover that covers the turbine runner and the lock-up clutch and that couples the pump impeller with the crank shaft and the rotor. The front cover may have an axially extending intermediate portion. The motor may be disposed radially outward of the intermediate portion, and the lock-up clutch may be disposed radially inside of the intermediate portion. Thus, the motor can be protected against loss of efficiency due to contact with hydraulic fluid by separating the motor from the lock-up clutch with the front cover and isolating the motor from the hydraulic fluid in inner portions of the hydraulic power transmission. At the same time, the radial dimension need not be increased to allow a reduction of the axial dimension.
A sensor for detecting a rotational position of the rotor may be disposed radially inside of the stator at a position that is substantially axially aligned with the lock-up clutch. Since the sensor detects the rotational position of the rotor, the efficiency of the motor can be improved. While the motor can be reliably prevented from rotating in reverse when the engine is being started, no additional axial space for installation of the sensor is required. Thus, the drive unit need not be increased in total length.
In the above aspect of the invention, the motor may be stored in a motor housing, and the stator may be fixed to the motor housing. The motor housing may be disposed between the engine and a housing containing the hydraulic power transmission. Since the motor housing for storing the motor is disposed between the engine and the housing for the hydraulic power transmission, there is no need to modify the torus of the hydraulic power transmission or the speed-change mechanism. Also, the motor including the motor housing can be constructed as a sub-assembly. Further, it is possible to manufacture the drive unit relatively easily without substantial modification of pre-existing conventional production lines, and provide flexible applicability to a great variety of engines and vehicles.
The hydraulic power transmission may be a torque converter including a turbine runner, a pump impeller and stator, whereby the torque of the vehicle is increased by the torque converter during takeoff. Thus, the vehicle can be reliably started in motion by means of the motor.
The motor may be a motor-generator that also functions as a generator. The motor-generator is directly coupled to the crank shaft of the engine, whereby the wheels are driven by the motor either by itself or in cooperation with the internal combustion engine. The motor-generator also functions as a generator for increasing the effect of an engine brake and performing the function of regeneration brake. Furthermore, the motor-generator also functions as a starter motor for starting the internal combustion engine. Thus, with a simple construction that does not necessitate any special starter motor, the engine need not be run at idle. In combination with the above functions of driving the vehicle and applying a regeneration brake, it becomes possible to reduce exhaust emissions and further improve fuel efficiency.
The predetermined clearance between the rotor and the hydraulic power transmission may be 0.8 to 3.5 mm whereby the rotor can be reliably prevented from being pressed by and interfering with the stator due to deformation of the hydraulic power transmission resulting from changes in centrifugal hydraulic pressure and so on. Also, the motor housing and thus the hybrid-vehicle drive unit need not be increased in size. Further, the clearance makes it possible to prevent the permanent magnet from becoming demagnetized due to generation of heat by the torque converter. Furthermore, the clearance makes it possible to prevent trash such as iron powder from flaking off the permanent magnet of the rotor and accumulating in the lock-up clutch disposed in the front cover of the torque converter. As a result, the lock-up clutch can operate without hindrance.